Vortex generators?

One interesting application I heard from Mike Opitz was the
adding of
turbulators forward of the hinge line of the rudder on a Grob
Twin. He reported
a remarkable improvement in feel and handling.
FWIW
UH

Since my name was brought up, I just want to mention that the
Grob airfoils were of the generation before turbulated airfoils came
out. Therefore, the Grob airfoils have tended to incur the large
laminar separation bubbles that are so typical of that earlier
generation. Some glider repair shops in Europe started
experimenting with retrofitting the Z-tape turbulators to gliders with
the older airfoils in hopes of minimizing how far forward the laminar
separation bubbles would creep, thus improving the performance.

In the case of the Grob gliders, it was discovered that putting the
Z-tape in front of the control surfaces can noticeably increase their
efficacy on some of the gliders, thus improving handling
characteristics.

Although Grob went bankrupt, the German glider repair center LTB
Lindner has picked up all of the rights to the Grob glider line, to
include molds, spares, and just about anything else that one would
need for true factory support. If they don't have a part, they can
manufacture one for you as well.

This brings me to UH's point about modifications to certified
aircraft. LTB Lindner has Service Letter #SL-12 published on their
web site which covers the LEGAL application of mylar seals and Z-
tape to all Grob gliders. Just go into the service letter, and it will
show you how and where one can LEGALLY apply the newer seals
and Z-tape.

http://www.ltb-lindner.com/service-letter.html

From personal experience, I can say that the Z-tape makes a very
noticeable difference in the handling of our club's Twin Astirs (Twin
1's). For anyone looking through previous old internet posts, you
will find that some people had gripes with the Twin 1's handling. I
would hazard a guess that those complainers had been flying Twin
Astirs that were not Z-tape equipped.

Last year at the Elmira Nationals, Erik Mann (P3) approached me
about the handling of his ACA (Blairstown, NJ) Twin Astir. I just
referred him to SL-12, and told him to talk to me after he
accomplished it. They did it over the winter. This year at the
Sports Class Nationals, I believe the quote from him was something
like "It's like it's a whole different glider. I actually have people that

like flying it now." Then, he told me that they hadn't even done the
rudder yet. I told him that the rudder would show a bigger
handling improvement than the ailerons if he were to do it...

This is a case where you don't have to experiment because someone
has already done it, and they got it certificated as well - a simple
solution to an issue that once had many pilots aggravated...

RO